Head-up display system for displaying image information and its calibration.

Description

[0001] The invention relates to a head-up display system, a method for calibrating the head-up display system and its use.

[0002] Vehicles, especially passenger cars, are increasingly being equipped with so-called head-up displays (HUDs). Head-up displays are designed to present visual information to the viewer, i.e., the driver. Using a projector as the image source, for example, located in the dashboard or roof area, images are projected onto the windshield, reflected there, and perceived by the driver as a virtual image (from their perspective) behind the windshield. This allows important information to be projected into the driver's field of vision, such as the current speed, navigation instructions, or warnings, which the driver can perceive without having to take their eyes off the road. Head-up displays can thus significantly contribute to improving road safety.

[0003] Windshields typically consist of two panes of glass laminated together with a thermoplastic film. If the surfaces of the glass panes are to be positioned at an angle, it is common to use a thermoplastic film with a non-constant thickness. This is also known as a wedge-shaped film or wedge film. The angle between the two surfaces of the film is called the wedge angle. The wedge angle can be constant across the entire film (linear thickness variation) or change depending on the position (non-linear thickness variation).

[0004] The problem with the head-up display described above is that the projected image is reflected off both surfaces of the windshield. As a result, the driver not only perceives the desired main image, which is caused by the reflection off the inner surface of the windshield (primary reflection), but also a slightly offset, usually less intense secondary image, caused by the reflection off the outer surface of the windshield (secondary reflection). This problem is generally solved by positioning the reflective surfaces at a deliberately chosen angle to each other, so that the main image and the secondary image (ghost image) are superimposed, thus making the secondary image (ghost image) less noticeable.

[0005] It is also known to coat windshields with transparent, electrically conductive coatings. These coatings can act as IR-reflective coatings to reduce the heating of the vehicle interior and thus improve thermal comfort. The coatings can also be used as heated coatings by connecting them to a voltage source, causing an electric current to flow through the coating. Suitable coatings contain conductive, metallic layers based on silver.

[0006] Windshields with conductive coatings within the laminated glass present a problem when used with head-up displays: the conductive coating creates an additional reflective interface for the projector image. This results in another unwanted secondary image, also known as layer reflection or layer "ghosting".

[0007] DE102014005977 discloses a HUD projection arrangement with a coated windshield. To avoid interference images, it is proposed to filter out the near-infrared light components from the imaging light beams while maintaining a sharp virtual image. However, this solution has the disadvantage that the projector must have additional infrared absorption elements in the beam path.

[0008] DE 102005 037797 A1, US 2011 / 267700 A1 and DE 10 2013 219556 A1 each contain a Head-Up Display System in which a correction image is generated.

[0009] The invention is based on the objective of providing a head-up display system which has a composite screen with an electrically conductive coating, whereby any interfering effect of the layer reflection generated by the coating should be minimized as much as possible.

[0010] The object of the present invention is achieved according to the invention by a head-up display system according to claim 1. Preferred embodiments are described in the dependent claims.

[0011] The head-up display (HUD) system according to the invention for displaying image information to a viewer comprises an image transmitter for emitting a first image, and a projection surface comprising a portion of a composite screen for deflecting a projection of the image. The head-up display system according to the invention also includes calibration means for detecting a deviation between the first image and the projected image. The calibration means have sensing means for detecting the reflective properties of the composite screen. The image transmitter is designed to generate a corrective image depending on the deviation.

[0012] A correction image is an image emitted by the image source that has undergone electronic pre-distortion or warping of the initial image. This distortion or warping is based on a previously measured deviation between the initial image and its projection. The correction image compensates for this measured deviation. Such electronic distortion is also known as pre-distortion or warping. In other words, the correction image is an image that has undergone electronic pre-distortion of the initial image. This compensation of the interfering reflection significantly improves the sharpness of the projected image.

[0013] An image transmitter can be understood to be an imaging device such as a projector, LCD display, or TFT display. For the purposes of this invention, image information is understood to be information that is presented to the viewer in the form of images. An image can contain digital image data.

[0014] The calibration devices include sensors used to determine the reflection properties. They also incorporate a software component for detecting distortion in the initial image. This software component can be stored on an external, hardware control unit, such as a computer. The control unit can include an input / output interface, allowing a user to operate the head-up display system and the calibration devices. The software component controls the sensors and the image sensor, as well as storing and analyzing image data. This has the advantage of influencing the emitted image in such a way that the projected image is clearer and of higher quality.

[0015] This image data, particularly distortion data, is transmitted to the image sensor. The image sensor has an interface to which the control unit sends the image data. Such an interface can be easily implemented on the image sensor, and the image data can be made available to the image sensor in a straightforward manner.

[0016] The acquisition means can include a storage medium in which the image data of the individual images can be stored. The calibration means can also include a photographic device for capturing images. The device for capturing images can be a single camera or a camera system with multiple cameras. In particular, the software component serves to control the device for capturing images, to store images, and to evaluate the images captured by the device. The evaluation of the captured images is preferably carried out by means of a matrix calculation.

[0017] Advantageously, the image sensor is designed to generate the corrective image. In particular, the corrective image can be configured as at least a partial overlap of the primary reflection, secondary reflection, and / or the layer reflection (ghost). This has the advantage of giving the projected image a distinct depth effect.

[0018] The composite pane comprises an outer pane and an inner pane bonded together by a thermoplastic interlayer. The surface of the inner pane facing the interlayer has a transparent, electrically conductive coating. This coating can include at least one metallic and several dielectric layers, which essentially determine the reflective properties of the composite pane, particularly its reflective color. The number, thickness, and composition of the layers can influence the reflective color of the composite pane. The reflectance of the coating is not constant across the color spectrum but exhibits a maximum in one or more wavelength ranges of the visible spectrum. This results in a color shift from white light to a specific color, which is referred to as the reflective color.

[0019] The calibration system is designed such that the generation of the correction image depends on the reflection color of the laminated glass or the thickness of the inner pane. A color from the color spectrum can be selected by amplifying the emission of a specific wavelength of light. Based on the reflection color, the control unit selects a wavelength range of light that is amplified in the correction image and transmits this image data to the image sensor. The color of the initial image is modified to compensate for the reflective properties of the coating. For example, true-to-life colors (e.g., white) can be reproduced in the correction image by having the image sensor amplify the emission of a complementary color (e.g., blue) to the reflection color (e.g., red) of the laminated glass. The color of the correction image is precisely matched to the reflection color of the laminated glass.

[0020] The laminated glass can be designed as a vehicle windshield. The laminated glass is intended to separate the interior from the external environment through an opening, particularly a vehicle window opening. For the purposes of the invention, the term "inner glass" refers to the pane of the laminated glass facing the interior (vehicle interior). The term "outer glass" refers to the pane facing the external environment.

[0021] The thickness of the interlayer varies, at least section by section, along the vertical path between the bottom and top edges of the composite panel. "Section by section" here means that the vertical path between the bottom and top edges of the composite panel has at least one section where the thickness of the interlayer changes depending on the location. However, the thickness can also change in several sections or along the entire vertical path. "Vertical path" refers to the path between the bottom and top edges with a direction essentially perpendicular to said edges. An interlayer with variable thickness is typically called a wedge foil. The angle between the two surfaces of the interlayer is called the wedge angle. If the wedge angle is not constant, the tangents to the surfaces must be used to measure it at a given point.

[0022] When an image is projected onto a composite disc, the desired first virtual image is generated by reflection off the inner surface of the inner disc, the side facing away from the interlayer. The unreflected portion of the beam passes through the composite disc and is reflected a second time off the outer surface of the outer disc, also facing away from the interlayer. This creates a second virtual image (ghost image). If the disc surfaces were parallel, the image and ghost image would appear offset from each other, which would be distracting for the viewer. Due to the wedge angle, the second virtual image is essentially superimposed spatially on the first, so that the viewer perceives only a single image.

[0023] The laminated glass pane has a transparent, electrically conductive coating on the surface of the inner pane facing the intermediate layer. This coating creates an additional interface with a significant change in the refractive index. This results in another reflective interface for the light beam from the image sensor. Consequently, the coating generates another unwanted ghost image, known as interlayer reflection.

[0024] A transparent coating is understood to be a coating that has an average transmission in the visible spectral range of at least 80%, meaning that it does not significantly restrict the view through the pane.

[0025] The inner and outer panes have asymmetrical thicknesses. An asymmetrical thickness combination is an arrangement of inner and outer panes where the two panes can have different thicknesses. Other asymmetrical thickness combinations (inner pane / outer pane) can have the following values: 1.6 mm / 2.1 mm; 1.4 mm / 1.8 mm; 1.4 mm / 2.1 mm; 2.1 mm / 2.6 mm; 1.0 mm / 1.4 mm.

[0026] The inner disc preferably has a thickness of less than 1.6 mm, so that the total thickness of the composite disc can be at least 4.0 mm to 6.0 mm, preferably 4.4 mm. Due to the wedge angle according to the invention, the thickness of the composite disc is not constant. The total thickness within the meaning of the invention is measured at the thinnest side edge, i.e., typically at the bottom edge of the composite disc. The total thickness is therefore the minimum total thickness that occurs.

[0027] The laminated glass is preferably curved in one or more spatial directions, as is common for automotive windshields, with typical radii of curvature ranging from about 10 cm to about 40 m. However, the laminated glass can also be flat, for example, if it is intended as a windshield for buses, trains, or tractors.

[0028] The area of ​​the composite screen intended to be illuminated by the projector to generate the virtual image is also referred to as the HUD area of ​​the composite screen. Advantageously, the geometry of the composite screen in the HUD area can have a vertical radius of curvature between 5 and 15 meters, and a horizontal radius of curvature between 1 and 5 meters.

[0029] The head-up display system preferably includes an optical module for deflecting the correction image generated by the image sensor towards the composite screen. The optical module can be designed as a combiner, mirror, prism, and / or lens device.

[0030] The invention further comprises a method for calibrating a head-up display system, in which a first image is emitted by an image sensor, the first image is deflected by at least a portion of a composite screen as a projection surface, and the projection of the image is captured by calibration means. A deviation between the first image and the projection of the image by the calibration means is measured. Depending on the deviation, the image sensor generates a correction image. The correction image is an image in which electronic pre-distortion, deformation, and / or colorization of the first image has taken place.

[0031] The invention also includes the use of a head-up display system according to the invention in a motor vehicle, preferably a passenger car.

[0032] The invention is explained in more detail below with reference to a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

[0033] They show: Fig. 1 a composite disc as a component of a head-up display system according to the invention, Fig. 2 a head-up display system according to the invention, Fig. 3 a flowchart of an embodiment of the method according to the invention and Fig. 4 a schematic representation of a correction image.

[0034] Figure 1Figure 1 shows a laminated glass pane 10 as a component of a head-up display system according to the invention, which consists of an outer pane 1 and an inner pane 2, which are bonded together via a thermoplastic intermediate layer 3. The laminated glass pane 10 is intended as a windshield for a motor vehicle equipped with a head-up display. In its installed position, the outer pane 1 faces the external environment, and the inner pane 2 faces the vehicle interior.

[0035] Furthermore, it shows Fig. 1A projector 4 serves as the image source for the HUD system and is directed onto a section of the laminated glass 10. Within this section (HUD area), the projector 4 can generate images that are perceived by the viewer 5 (vehicle driver) as virtual images on the side of the laminated glass 10 facing away from them. The wedge angle in this section results in surfaces I, IV of the outer pane 1 and the inner pane 2 being inclined relative to each other. The thin inner pane 2 causes the layer reflection caused by the electrically conductive coating 6 to superimpose with the primary reflection caused on the inner surface of the windshield and the secondary reflection caused on the outer surface of the windshield, making these reflections indistinguishable from one another.

[0036] The outer pane 1 has an outer surface I, which, when installed, faces the external environment, and an inner surface II, which, when installed, faces the interior. Similarly, the inner pane 2 has an outer surface III, which, when installed, faces the external environment, and an inner surface IV, which, when installed, faces the interior. The inner surface II of the outer pane 1 is connected to the outer surface III of the inner pane 2 via the intermediate layer 3.

[0037] The thickness of the intermediate layer 3 increases continuously in the vertical direction from the bottom edge to the top edge of the composite disc. For the sake of simplicity, the increase in thickness is shown linearly in the figure, but more complex profiles are also possible. The intermediate layer 3 is formed from a single PVB film (a so-called wedge film with variable thickness). The wedge angle α is 0.25 mrad to 0.8 mrad, preferably 0.35 mrad to 0.65 mrad. In HUD systems with a large field of view, such as an augmented reality (AR) HUD system, wedge angles of 0.1 mrad to 0.3 mrad are also used. AR HUD systems are HUD systems that use computer-aided enhancement of a user's perception of reality.

[0038] For a wedge angle of 0.5 mrad and a laminated pane with a height of 1 meter, which is the average height of a car windshield, this equates to a thickness change of approximately 0.5 mm (e.g., 0.76 mm at the bottom edge and 1.26 mm at the top edge of the laminated pane). The thickness of the interlayer depends not only on the wedge angle but also on the pane height. With a preferred glass combination of inner / outer panes of 1.6 mm / 2.1 mm, the total glass thickness would be 4.46 mm at the bottom edge and 4.96 mm at the top edge of the laminated pane.

[0039] Due to the wedge-shaped shape of the intermediate layer 3, the two virtual images generated by the reflection of the projector image off surfaces I and IV are superimposed. The secondary reflection therefore does not appear offset from the primary reflection, thus avoiding disruptive reflections. Instead, the layer reflection creates another virtual image, which, through its superposition with the primary and secondary reflections, results in a single virtual image.

[0040] The laminated glass 10 also features an electrically conductive coating 6 on the outer surface III of the inner glass 2. The coating 6 is IR-reflective and designed to reduce the heating of the vehicle interior caused by the IR component of solar radiation. The coating 6 is, for example, a thin-film stack containing two or three layers of silver and other dielectric layers that, as anti-reflective, blocking, or surface-matching layers, optimize the optical, electrical, and / or mechanical properties of the coating. The dielectric layers of the conductive coating 6 contain, for example, silicon nitride, silicon oxide, zinc oxide, tin-zinc oxide, and aluminum nitride.

[0041] The coating 6 represents a further reflective interface inside the composite disk 10, at which the correction image according to the invention is reflected once again.

[0042] The inner pane 2 is made of soda-lime glass and has a very small thickness, for example 1.6 mm. This ensures that the spatial offset between primary reflection and layer reflection is small, and that the virtual images overlap in such a way that a sharp and color-accurate corrected image is formed in the eye of the viewer 5.

[0043] The outer pane 1 is also made of soda-lime glass and has a significantly greater thickness, for example 2.1 mm. This ensures that the laminated pane 10 as a whole has sufficient mechanical stability, impact resistance and torsional rigidity.

[0044] The minimum thickness of the intermediate layer 3 is, for example, 0.76 mm (measured at the bottom edge U). Here, the intermediate layer 3 is formed by a single, wedge-shaped PVB film. However, a multi-layered structure of the intermediate layer 3 is also conceivable, for example, a 0.36 mm thick PVB film of constant thickness, a 0.76 mm thick PVB wedge film, and an intermediate 0.05 mm thick PET film.

[0045] The total thickness of the composite disc 10 is therefore approximately 4.5 mm. The total thickness is measured at the thinnest side edge, namely the bottom edge.

[0046] Figure 2Figure 1 shows a head-up display system according to the invention with calibration means. The calibration means comprise a sensor 7 for capturing a projection of the first image and a control unit 8 with a software component 9 for controlling the sensor 7 and for evaluating the projection. The sensor 7 is configured as a camera system with multiple cameras for recording the projection. Image data from the recording is then forwarded to the control unit 8. The control unit 8 is a computer with several compatible interfaces suitable for receiving image data from the sensor 7 and for exchanging image data with the image generator. Such interfaces are wired and / or wireless and are suitable for operating according to one of the following standards: WLAN (Wi-Fi, IEEE 802.11), NFC, or Bluetooth.Furthermore, the control unit 8 has a user interface where a user of the head-up display system can interact with the calibration device.

[0047] Projector 4 emits a first image, which is deflected as a virtual image via the composite screen 10. The camera system of the detection device 7 captures the virtual image and stores its image data. This image data is then transmitted via an interface to the control unit 8. The control unit 8 receives the image data of the virtual image and compares it with the image data of the first image emitted by projector 4. The software component 9 performs matrix calculations to evaluate the image data, and the results are stored in the control unit 8. The evaluated image data is then transmitted back to projector 4.

[0048] Fig. 3shows a flowchart of an embodiment of the inventive method for calibrating a head-up display system according to the invention.

[0049] In step 12 of the process, a first image is emitted by projector 4. This first image is deflected by at least a portion of a composite disc acting as a projection surface and, in step 13, is captured as a projection of the first image by a calibration device. The calibration device consists of a camera system 7, which records the projection of the first image and, in step 14, transmits it to the control unit 8. The control unit 8 can be configured as an external computer with a storage medium. The control unit 8 has a software component 9, which, in step 15, compares and evaluates the projection of the first image with the image emitted by projector 4. The evaluation of the images in the form of image data is performed by the software component 9 using matrix calculations. In step 16, the result of the evaluation reveals a deviation, which is transmitted from the control unit 8 to projector 4.

[0050] The deviation measured with calibration fluid between the first image and the projection of the first image can result in distortion, deformation, discoloration, or distortion of the first image. Based on this deviation, in step 17, projector 4 generates a correction image from the first image. The correction image is an image in which electronic pre-distortion, deformation, and / or colorization of the first image has taken place. Such a pre-setting of projector 4 ensures that the correction image is displayed sharply and with accurate colors. The information in the virtual image is clearly and distinctly recognizable to the viewer.

[0051] Figure 4Figure 1 shows the result of an evaluation. The evaluation may reveal that the design of the first image is modified. The corrected image is then designed such that the primary, secondary, and layer reflections partially overlap and, ideally, touch. Through such a superposition of reflections, for example, a circular cutout can be displayed in a solid surface by emitting an oval base shape as a corrected image from projector 4. The superposition of the oval base shape with the secondary and layer reflections of the oval base shape creates the visual impression of a circular cutout for the viewer. Images can be superimposed into the viewer's field of vision that appear to be part of the viewer's surroundings. The application of the head-up display system according to the invention is particularly advantageous for navigation by the viewer or driver of a vehicle.A navigation direction can be represented as a directional arrow by projecting an image of the directional arrow into the driver's line of sight, giving the driver the impression that the directional arrow is lying on their lane.

[0052] If projector 4 fails to account for a deviation previously detected by the calibration system when generating an image, the image is reflected off the laminated glass. This reflection, due to primary, secondary, and layer reflection, creates three virtual images that do not align correctly. For the driver's eye 5, this would result in a blurry, color-inaccurate image containing unrecognizable information. Reference symbol list:

[0053] (1) Outer pane (2) Inner pane (3) Thermoplastic interlayer (4) Projector as image transmitter (5) Viewer / Vehicle driver (6) Electrically conductive coating (7) Detection device (8) Control unit (9) Software component (10) Composite pane (11) Head-up display system (12) to (17) Process step (I) Outer surface of the outer pane 1 facing away from the intermediate layer 3 (II) Inner surface of the outer pane 1 facing towards the intermediate layer 3 (III) Outer surface of the inner pane 2 facing towards the intermediate layer 3 (IV) Inner surface of the inner pane 2 facing away from the intermediate layer 3

Claims

1. Head-up display system (11) for representing image information for an observer comprising: - a composite pane (10), wherein the composite pane (10) comprises an outer pane (1) and an inner pane (2) joined to one another via a thermoplastic intermediate layer (3) and a transparent, electrically conductive coating (6) on the surface (III) of the inner pane (2) facing the intermediate layer (3), - an image encoder (4) for emitting a first image, - a projection area comprising a portion of the composite pane (10) for deflecting a projection of the first image, wherein calibration means (7, 8, 9) are provided for ascertaining a deviation between the first image and the projection of the first image, which have capturing means (7) for capturing reflection properties of the composite pane (10), wherein the image encoder (4) is provided for generating a correction image having a predistortion as a function of the deviation, wherein the calibration means (7, 8, 9) are provided for determining a reflection color of the composite pane (10), wherein the calibration means (7, 8, 9) have a software component (9) for determining a distortion of the first image as a function of the reflection color or the thickness of the inner pane (2), wherein the image encoder (4) has an interface for transmitting image data of the software component (9), and wherein the image encoder (4) is provided for generating the correction image by means of the first image and the distortion.

2. Head-up display system (11) according to claim 1, characterized in that the calibration means (7, 8, 9) include a control unit (8), wherein the control unit (8) is provided for selecting a wavelength range of light, and the image encoder (4) is provided for emitting the correction image in the selected wavelength range.

3. Head-up display system (11) according to one of claims 1 or 2, characterized in that the composite pane (10) is a vehicle windshield.

4. Head-up display system (11) according to one of claims 1 through 3, characterized in that an optical module is provided for deflecting the correction image generated by the image encoder (4) in the direction of the composite pane (10).

5. Head-up display system (11) according to one of claims 1 through 4, characterized in that the projection area of the composite pane (10) has a vertical radius of curvature between 5 and 15 meters and / or a horizontal radius of curvature between 1 and 5 meters.

6. Head-up display system (11) according to one of claims 1 through 5, characterized in that the inner pane (2) and the outer pane (1) have asymmetric thicknesses.

7. Method for calibrating a head-up display system (11) according to one of claims 1 through 6, wherein a first image is emitted by an image encoder (4), wherein the first image is deflected by a portion of a composite pane (10) as a projection area and is captured as a projection of the first image by calibration means (7, 8, 9), wherein a deviation between the first image and the projection of the first image is measured by the calibration means (7, 8, 9) and the image encoder (4) is provided for generating a correction image as a function of the deviation.

8. Use of a head-up display system (11) according to one of claims 1 through 6 in a motor vehicle, preferably a passenger car.